#include<iostream>
#include<string>
using namespace std;

int main() {
	int i = 0, j = 0, a[100000]{0}, n = 0, f = 1, b = 0, d = 0;

	cin >> n;

	for (i = 0; i < n; i++) {
		cin >> a[i];
	}

	while (f == 1) {
		f = 0;
		for (i = 0; i < n - 1 - j; i++) {
			if (a[i] > a[i + 1]) {
				b = a[i];
				a[i] = a[i + 1];
				a[i + 1] = b;
				f = 1;
			}
		}
		j++;
	}

	d = a[1] - a[0];
	if(d != 0){
		for (i = 0; i < n - 1; i++) {
			if ((a[i + 1] - a[i]) != d) {
				f = 0;
				break;
			}
			if (i == (n - 2)) f = 1;
		}
	}

	if (f == 1) cout << "YES" << endl;
	else cout << "NO" << endl;

	return 0;
}